Maternal Condition and the Quality of Maternal Care in Vervet Monkeys

Abstract

Seemingly contradictory results on the relationship between maternal condition and the quality of maternal care can be resolved by the hypothesis that maternal rejection is a U-shaped function of maternal condition. Data from 160 vervet monkey (Cercopithecus aethiops sabaeus) mother-infant dyads living in captive social groups were used to evaluate the influence of maternal reproductive condition on mothcr-infant contact, maternal rejection and infant mortality. Reproductive condition was defined as Marginal, Prime and Average based on age, weight, and dominance rank. Marginal mothers were at the extremes of the reproductive age distribution (3 years old or over 14) or were below a critical body weight (3.9 kg), characteristics that are associated with low rates of fertility in the study population. Prime mothers were in the top third of the female dominance hierarchy and of prime age (5-13), characteristics associated with higher than average fertility. Both marginal mothers and prime mothers had similar high rates of maternal rejection and low rates of ventral contact and proximity with their infants. Compared to mothers in the two extreme groups, mothers in average reproductive condition were significantly less rejecting and played a larger role in maintaining contact with their infants. Rates of maternal rejection, mother-infant contact, responsibility for contact, and the percentage time that infants spent on nonmaternal caretakers were all significantly related to maternal condition in U-shaped or inverted U-shaped functions. The infant mortality due to maternal abandonment or neglect was highest in the marginal group and was related to low body weight of the mother. We conclude that mothers in marginal condition limited maternal care to restore their own health, often at the expense of infant mortality, whereas mothers in prime condition used rejection to shorten the interval to the ncxt conception, without suffering higher rates of infant mortality than average mothers.